PET detector, setting method and detecting method thereof

ABSTRACT

A PET detector and method thereof are provided. The PET detector may include: a crystal array including a plurality of crystal elements arranged in an array and light-splitting structures set on surfaces of the plurality of crystal elements, the light-splitting structures jointly define a light output surface of the crystal array; a semiconductor sensor array, which is set in opposite to the light output surface of the crystal array and is suitable to receive photons from the light output surface, the semiconductor sensor array comprises a plurality of semiconductor sensors arranged in an array.

TECHNICAL FIELD

The present disclosure relates to the technical field of opticaldetecting, to be more specific, to an apparatus and a method for a PETdetector.

BACKGROUND

Generally, positron emission tomography (PET) detectors have been set invarious large medical devices such as, positron emissiontomography-computed tomography (PET-CT) devices, positron emissiontomography-magnetic resonance imaging (PET-MRI) devices, in which PETtechnologies are applied. PET detectors are used to receive γ raysgenerated from a patient's body and to provide information related tothe locations where photons are excited by γ rays in the sensors toother components of the large medical devices, so that the othercomponents of the large medical devices may process appropriately basedon the location information.

As shown in FIG. 1, currently, a PET detector typically includes acrystal array 102, an avalanche photo diode (APD) array 104 coupled withthe crystal array 102, and a light guide 106 which is set between thecrystal array 102 and the APD array 104. Among them, the crystal array102 is formed by multiple crystal elements, which are arranged accordingto a certain design. The APD array 104 is formed by multiple APDs, whichare arranged according to a certain design. Each APD contacts with atleast one crystal element.

The γ rays generated in the patient's body are received by a certaincrystal element in the crystal array 102. The γ rays excite photonsinside the crystal element. The photons transmit among several crystalelements in the crystal array 102, and ultimately enter into the APDarray 104 through the light guide 106. And then they are received by theAPD array.

When the γ rays excite photons inside the crystal element, opticaltransmission loss may be caused by the light guide 106. As such, only aportion of the excited photons may enter into the APD array 104,resulting in a lower resolution of the PET detector.

SUMMARY

The embodiments of the present invention is intended to solve theproblem to enhance the resolution of a PET detector.

To solve the problem, according to embodiments of the present inventiona PET detector is provided, which comprises:

a crystal array, which comprises a plurality of crystal elements and alight splitting structure mounted on a surface of each of the pluralityof crystal elements, the light splitting structures defining a lightoutput surface of the crystal array jointly;

a semiconductor sensor array comprising a plurality of semiconductorsensors for receiving photons from the light output surface, each of theplurality of semiconductor sensors contacting at least a portion of thelight output surface of the crystal array.

In some embodiments, more than one of the plurality of crystal elementsin the crystal array may be coupled with one semiconductor sensor of thesemiconductor sensor array.

In some embodiments, at least one semiconductor sensor of thesemiconductor sensor array may be coupled with each of the plurality ofcrystal elements in the crystal array.

In some embodiments, the coupling comprises a contact between thesemiconductor sensors and the crystal elements directly or through anadhesive material.

In some embodiments, a center-of-gravity of the semiconductor sensorarray may coincide with a center-of-gravity of the crystal array.

In some embodiments, the semiconductor sensor array may completely orpartially cover the light output surface.

In some embodiments, the light-splitting structure may include alight-reflective membrane or a white light-reflective coating.

In some embodiments, the PET detector further comprises a firstamplifier, an input terminal of the first amplifier being connected withan output terminal of a semiconductor sensor in a predetermined row ofthe semiconductor sensor array.

In some embodiments, the PET detector further comprises a secondamplifier, an output terminal of the first amplifier being connectedwith an output terminal of a semiconductor sensor in a predeterminedcolumn of the semiconductor sensor array.

In some embodiments, the light-splitting structures on the surfaces ofthe crystal elements may be set based on light-receiving areas of thesemiconductor sensors, a relative positioning between the semiconductorsensors, relative positioning between the semiconductor sensors and thecrystal array.

In some embodiments, a resolution of the crystal elements in an imagemay relate to a number or positioning of the semiconductor sensors.

According to embodiments of the present invention, a method for settinga PET detector is further provided, which comprises:

adjusting an area of a light-splitting structure on each of a pluralityof crystal elements in a crystal array, the light-splitting structuresjointly forming a light output surface of the crystal array; and

setting the semiconductor sensor array in contact with at least aportion of the light output surface of the crystal array.

In some embodiments, the adjusting areas of light-splitting structuresset on each crystal element in the crystal array comprises:

adjusting a probability of photon occurrence in a crystal element;

if the probability of photon occurrence in the crystal element satisfiesa resolution condition, setting the area of the crystal elementaccording to the area of the light-splitting structure corresponding tothe probability of photon occurrence.

In some embodiments, the adjusting of the probability of photonoccurrence in the crystal element comprises,

adjusting the probability of photon occurrence in a first crystalelement according to the following equation:

${P(m)} = {\frac{N!}{{m!}{\left( {N - m} \right)!}}{p^{m}\left( {1 - p} \right)}^{({N - m})}}$

wherein N represents a total number of the photons excited in a secondcrystal element in the crystal array other than the first crystalelement, m represents a number of the photons excited in the firstcrystal element when N photons are excited in the second crystalelement, p represents a probability that when a photon is excited in thesecond crystal element the photon occurs in the first crystal element,and P represents a probability that m photons occur in the first crystalelement when N photons are excited in the second crystal element.

According to embodiments of the present invention, a detection method isfurther provided, which comprises:

providing a PET detector;

receiving a γ ray by a crystal element of the PET detector;

receiving photons excited by the γ ray in the crystal element by asemiconductor sensor of the PET detector;

determining a position where the γ ray generates the photons in thecrystal element according to an output of the semiconductor sensor.

In some embodiments, the determining of the position comprises using acenter-of-gravity readout method.

In some embodiments, a positron emission tomography (PET) detector isprovided. The PET detector may include:

a crystal array, the crystal array comprising a plurality of crystalelements; each of the plurality of crystal elements extending alongup-to-down direction, and having an upper side and a lower side, and asurrounding surface between the upper side and the lower side;

a light-splitting structure mounted on the surface of each of theplurality of crystal elements, the light-splitting structure corporatelywith the crystal array to define a light output surface; and

a semiconductor sensor array comprising a plurality of semiconductorsensors for receiving photons from the light output surface, each of theplurality of semiconductor sensors sharing at least a portion of thelight output surface of the crystal array.

Embodiments of the present invention may have the following features:

By setting light-splitting structures on the crystal elements, thetransmission distance of photons may be effectively shorten, compared tothat of photons in the case of setting light guide between the crystalarray and semiconductor sensors, therefore light transmission loss maybe avoided, and the resolution of the PET detector may be enhanced.

By coupling a portion of crystal elements in the crystal array with thecorresponding semiconductor sensors in the semiconductor sensor array,there is no need to couple every crystal element in the crystal arraywith its corresponding semiconductor sensor, which makes the setting ofthe number of semiconductor sensors more flexible. Therefore, when thesame number of crystal elements are used, less semiconductor sensors maybe used to satisfy the same resolution of crystal elements in the sameimage. Thus the cost of the PET detector may be reduced.

By setting the center-of-gravity of the semiconductor sensor array incoincidence with the center-of-gravity of the crystal array, the use ofthe center-of-gravity readout method to determine the location wherephotons are excited may be more convenient.

As the semiconductor sensor array may cover the light output surfacecompletely or partially, the setting of the number and positions ofsensors may be more flexible, therefore, when the same number of crystalelements is used, less semiconductor sensors may be used to satisfy thesame resolution of crystal elements in the same image. Thus the cost ofthe PET detector may be reduced.

By setting the first amplifier and the second amplifier, when thecenter-of-gravity readout method is used to determine the location wherephotons are excited, the location where photons are excited may bedetermined directly according to the output of the first amplifier andthe second amplifier, and it is not required to read every output ofsemiconductor sensors. Therefore the amount of data processed todetermine the location where photons are excited, and the difficulty todetermine the locations of photons may be reduced.

By adjusting the probability of photon occurrence in the whole crystalelement according to the equation

${P(m)} = {\frac{N!}{{m!}{\left( {N - m} \right)!}}{p^{m}\left( {1 - p} \right)}^{({N - m})}}$

and adjusting the area of a light-splitting structure on a correspondingcrystal element, a desired spatial resolution of images may be satisfiedmore rapidly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a longitudinal section of a PETdetector in related art.

FIG. 2 is a diagram illustrating a longitudinal section of a PETdetector according to one embodiment of the present disclosure.

FIGS. 3-7 are diagrams illustrating examples of a cross section of a PETdetector in accordance with some embodiments of the present disclosure.

FIG. 8 is a diagram illustrating a light-splitting structure coupled toa crystal element according to some embodiments of the presentdisclosure.

FIG. 9 is a diagram illustrating a transmission path of a photon betweentwo crystal elements according to one embodiment of the presentdisclosure.

FIG. 10 is a diagram illustrating a transmission path of a photonbetween two crystal elements according to another embodiment of thepresent disclosure.

FIG. 11 is a diagram illustrating the probability distribution ofphotons that appear inside a crystal element in the crystal array beforeadjusting a diagram illustrating the probability distribution of photonsthat appear inside a crystal element in the crystal array beforeadjusting in accordance with some embodiments of the disclosure.

FIG. 12 is a diagram illustrating a distribution of the probability thatphotons appear in a crystal element of a 1×10 crystal array afteradjustment of a PET detector in accordance with some embodiments of thedisclosure.

FIG. 13 is a structural diagram illustrating a cross section of a PETdetector according to some embodiments of the present disclosure.

FIG. 14 is a diagram illustrating a distribution of the probability thatphotons appear in each crystal element of the PET detector in FIG. 13.

FIG. 15 is a two-dimension image of each crystal element locationgenerated by the PET detector in FIG. 13.

FIG. 16 is a flow chart illustrating a method for configuring a PETdetector according to one embodiment of the present invention.

FIG. 17 is a flow chart illustrating a method for providing a PETdetector according to one embodiment of the present invention.

DETAILED DESCRIPTION

In a PET detector structure as shown in FIG. 1, after a γ ray generatesphotons in a crystal element, the photons may enter an APD array 104through a light guide 106. The arrangement of the light guide 106 mayincrease the distance of the photon transmission, and may cause someloss in optical transmission and a decrease in the PET detectorresolution.

The above-mentioned features of the present disclosure will becomefurther apparent from the following detailed description of the specificembodiment of the present invention with reference to the accompanyingdrawings.

FIG. 2 illustrates an exemplary PET detector according to someembodiments of the present disclosure. As illustrated, the PET detectormay include a crystal array and a semiconductor sensor array.

The crystal array may include multiple crystal elements 202 arranged inan array, and optionally a light-splitting structure 204 that is coupledto the surface of the crystal elements 202. The light-splittingstructures 204 mounted on the multiple crystal elements 202 may define alight output surface 206 of the crystal array. The semiconductor sensorarray may be mounted in opposite to the light output surface 206 of thecrystal array. The semiconductor sensor array may comprise multiplesemiconductor sensors 208 arranged in an array. The semiconductor sensorarray is integrated on the driver board 210. The driver board 210 isconnected to the semiconductor sensor 208, applicable to drive theoperation of the corresponding semiconductor sensor.

Each of the crystal elements 202 may correspond to a light outputsurface. A light output surface of a given crystal element 202 may referto a surface of the given crystal element through which a photon exitsthe given crystal element to enter corresponding a semiconductor sensor208 corresponding to the given crystal element. In some embodiments ofthe present disclosure, the light output surfaces 206 may include thelight output surfaces of crystal elements 202.

The crystal array may include any suitable number of crystal elements202. The crystal elements 202 may be arranged in any suitable manner. Asan example, the crystal array comprises three or more crystal elements202. As another example, as shown in FIGS. 3-5, the crystal elements 202may be arranged in an 8×8 array, an 8×9 array, an 8×19 array, etc. Insome embodiments, the number of crystal elements 202 in the crystalarray may be determined based on the dimensions of the PET detector 200.For example, a larger PET detector may include a greater number ofcrystal elements 202. Various numbers of crystal elements may correspondto various sizes of PET detectors.

Each crystal element 202 may be made of various materials, such as oneor more of bismuth germanium oxide, lutetium oxyorthosilicate, lutetiumyttrium oxyorthosilicate, lutetium gadolinium oxyorthosilicate,gadolinium orthosilicate, yttrium orthosilicate, barium fluoride, sodiumiodide, cesium iodide, lead tungstate, yttrium aluminum perovskite,lanthanum (III) bromide, lanthanum (III) chloride, lutetium aluminumperovskite, lutetium pyrosilicate, lutetium aluminate and lutetiumiodide, etc.

A γ ray may excite one or more photons in the crystal array. Forexample, the γ ray may excite multiple photons in a crystal element 202(also referred to herein as the “first crystal element”). One or more ofthe excited photons may travel towards a light-splitting structure 204coupled to the first crystal element. Upon receiving one or more of theexcited photons, the light-splitting structure 204 may change the pathof the received photons. For example, the received photons may bereflected by the light-splitting structure and may then enter asemiconductor sensor corresponding to the first crystal element througha surface of the first crystal element (e.g., the light output surfaceof the crystal element 202 that may be used to define light outputsurface 208). In some embodiments, one or more of the photons excited inthe first crystal element may enter into a semiconductor sensorcorresponding to another crystal element in the crystal array (alsoreferred to herein as the “second crystal element”) through a surface ofsecond crystal element (e.g., a light output surface of the secondcrystal element that may be used to define the light output surface206). In some embodiments, the semiconductor sensor corresponding to thefirst crystal element and the semiconductor sensor corresponding to thesecond crystal element may or may not be the same. In some embodiments,a particular semiconductor sensor of the semiconductor sensor array mayreceive photons from a surface of a crystal element used to define thelight output surface, or from respective surfaces of multiple crystalelements used to define the light output surface.

In some embodiments, as the semiconductor sensors array receive photonsfrom the light output surface of the crystal array, the semiconductorsensors may be coupled to the crystal elements in any suitable manner.For example, the semiconductor sensors may contact with the crystalelements through one or more adhesive materials. Examples of theadhesive material include silicone grease and/or any other suitablematerial that may be used to couple a crystal element and asemiconductor sensor.

As another example, a portion of the crystal elements of the crystalarray may be coupled to one or more semiconductor sensors 208 of thesemiconductor sensor array, which allows the semiconductor sensors toreceive photons from the light output surface of the crystal array.Wherein the portion of crystal elements of the crystal array maycorrespond to one or more semiconductor sensors.

FIG. 3 is a schematic diagram of a cross section of a PET detector inaccordance with some embodiments of the disclosure. In some embodiments,the PET detector of FIG. 3 may be the PET detector as described above inconnection with FIG. 2. The crystal elements and the semiconductorsensors of FIG. 3 may be the same as one or more of the crystal elements202 and the semiconductor sensors 206 of FIG. 1, respectively.

As illustrated, the crystal array of the PET detector may be and/orinclude an 8×8 array of crystal elements 202. The semiconductor sensorarray may be and/or include a 2×2 array of semiconductor sensors. Thecrystal elements 202 may include one or more crystal elements 202 a thatare coupled to one or more semiconductor sensor 208. The crystalelements may also include one or more crystal elements 202 b that arenot coupled to a semiconductor sensor 208. In some embodiments, aportion of the crystal array (e.g., one or more crystal elements 202 a)may correspond to (e.g., be coupled to) a semiconductor sensor 208. Forexample, as shown in FIG. 3, four portions of the crystal array maycorrespond to four semiconductor sensors 208 of the semiconductor sensorarray, respectively. In some embodiments, after the γ ray excitesphotons within a crystal element 202 b that is not coupled to asemiconductor sensor 208, the photons may be transmitted into one ormore crystal elements 202 a (e.g., crystal elements that are covered byone or more semiconductor sensors 208) via the light-splitting structurecoupled to a surface of the crystal element 202 b. A semiconductorsensor corresponding to the crystal element 202 a may then receive thephotons.

According to another embodiment of the present disclosure, at least onesemiconductor sensor of the semiconductor sensors array is coupled tothe corresponding crystal elements of the crystal array, such that thesemiconductor sensors may receive photons from the light output surfaceof the crystal array. Wherein within the semiconductor array, one ormore semiconductors may have corresponding crystal elements within thecrystal array, so long as one semiconductor sensor of the semiconductorsensors array may receive photons from the light output surface of thecrystal array.

FIG. 6 illustrates an example of the cross section of a PET detector.The PET detector may include a crystal array of 8×8 crystal elements 202and a semiconductor sensor array of 2×2 semiconductor sensors (e.g.,semiconductor sensors 2081, 2082, 2083, and 2084). In some embodiments,one or more of the semiconductor sensors may or may not be coupled to acrystal element 202. A crystal element that is coupled to a givensemiconductor sensor is also referred to herein as a crystal elementcorresponding to the given semiconductor sensor. As an example,semiconductor sensor 2081 and/or semiconductor sensor 2082 may becoupled to one or more crystal elements 202 in the crystal array. Asanother example, semiconductor sensor 2083 and/or semiconductor sensor2084 are not coupled to a crystal element 202 in some embodiments.

In another embodiment of the present invention, the semiconductor sensorarray covers the light output surface of the crystal array completely orpartially, so that the semiconductor sensor may receive photons at thelight output surface.

FIG. 7 illustrates an example of the cross section of the PET detectorin accordance with some embodiments of the disclosure. In someembodiments in which the semiconductor sensor array covers the lightoutput surface of the crystal array completely, each crystal element 202in the crystal array may be covered by the semiconductor sensor. Assuch, each crystal element 202 in the crystal array is coupled to atleast one semiconductor sensor 208 in the semiconductor sensor array andthus corresponds to the at least one semiconductor sensor. Thecorresponding semiconductor sensor may be part of the semiconductorsensors in the array or all of the semiconductor sensors in the array.For example, one or more semiconductor sensors 208 may be coupled with agiven crystal element 202 and thus correspond to the given crystalelement 202.

In some embodiments in which the semiconductor sensor array partiallycovers the light output surface of the crystal array, one or moreportions of the crystal array (e.g., one or more crystal elements) arecoupled to the corresponding semiconductor sensor 208. In an embodimentof the present disclosure, as shown in FIG. 3, each semiconductor sensor208 in the semiconductor sensor array is coupled with one or morecrystal elements 202 in the crystal array. The semiconductor sensorarray covers the light output surfaces of part of the crystal elementsin the crystal array. In another embodiment, as shown in FIG. 6, aportion of the semiconductor sensor array are coupled to the crystalelements in the crystal array. The portion of the semiconductor sensorarray may include one or more semiconductor sensors. The portion of thesemiconductor sensor array may cover the light output surfaces of one ormore crystal elements in the crystal array.

In order to determine the positions of the photons which are excited bythe γ ray inside the crystal elements according to the output of thesemiconductor sensors more conveniently, the center-of-gravity of thesemiconductor sensor array and the center-of-gravity of the crystalarray may be set coincidently. When the center-of-gravity of thesemiconductor sensor array and the center-of-gravity of the crystalarray coincide, the positions of the photons may be determined using thecenter-of-gravity readout method. As shown in FIGS. 3-5, thesemiconductor sensor array may include multiple semiconductor sensors208 that are arranged in an array. The crystal array comprises multiplecrystal elements 208 that are arranged in an array. As such, thecenter-of-gravity of the semiconductor sensor array and thecenter-of-gravity of the crystal array coincide. The center-of-gravityof the crystal array may be determined by a calculation of dimensions ofthe crystal array based on the center-of-gravity of the semiconductorsensor array. The positions of the photons may then be determined by thecenter-of-gravity of the crystal array.

In some implementations, the semiconductor sensor array may includethree or more semiconductor sensors. The semiconductor sensors may beand/or include photoresistors, photodiodes, phototransistors, and/or anyother suitable device that may be used as a semiconductor sensor inaccordance with embodiments of the present disclosure. Wherein theresolution of the crystal elements in the image is related to the numberand positions of the semiconductor sensors. In some implementations,persons skilled in the art may adjust the number and positions of thesemiconductor sensors in the above-mentioned embodiments according tothe requirement of the resolution of the crystal elements in the image.For example, as shown in FIGS. 3-5, the semiconductor sensor array mayinclude any suitable number of semiconductor sensors (e.g., four, five,eight, etc. semiconductor sensors) to achieve various resolutions of thecrystal elements in images generated by the PET detector.

The resolution of the crystal elements in the image may refer to theresolution of the corresponding position of each crystal element in theimage obtained by the PET detector. When the resolution of the crystalelements in the image is higher, the corresponding position of eachcrystal element is clearer, and the boundaries between differentpositions of the crystal elements are sharper.

As described above, the PET detector may have any suitable number ofsemiconductor sensors. The semiconductor sensors may be arranged invarious manners. For example, a semiconductor sensor of the PET detectormay or may not correspond to a crystal element in the crystal array. Assuch, embodiments of the present disclosure address the deficiencies ofexisting PET detectors by providing a PET detector with enhancedresolution and by reducing the number of semiconductor sensors used inthe PET detector.

In some embodiments, the PET detector may generate an optical signal andmay convert the optical signal into an electrical signal (e.g., usingthe semiconductor sensors on the base of inner photoelectric effect).Compared with the devices which convert optical signals into electricalsignals based on external photoelectric effect, the semiconductorsensors have the advantages of small size, light weight, imperviousnessto magnetic fields while working, etc.

For example, the common used diameter dimensions of PMTs which convertoptical signals into electrical signals based on external photoelectriceffect are ¾ inch, 1 inch and 1.5 inches. And the dimensions of diameterof semiconductor sensors are usually 3×3 mm² or 6×6 mm². When contactingthe crystal elements, the contact area of a 1-inch PMT is about 8×8 cm²,while that of a 6×6 mm² semiconductor sensor is about 2×2 cm². Thelarger the contact area of the crystal elements is, the more the numberof events received in unit time is, which means the detector's dead timebecomes longer and the signals would be more likely to pile up, thus thesensitivity of the PET detector gets worse. Calculations show that thenumber of events received by a 1-inch PMT in unit time is 16 times asmuch as that by a 6×6 mm² semiconductor. Under the same circumstance,the dead time of a PET detector with PMT sensors is about 2-3 times asmuch as that of a PET detector with semiconductor sensors. Therefore,the PET detector with semiconductor sensors has a higher sensitivity.Furthermore, the PET detector with semiconductor sensors as previouslydescribed may work free from the influence of magnetic fields, whichmakes it more convenient for the user.

In some embodiments, the light-splitting structures may be coupled tothe surface of the crystal elements in any suitable manner. For example,the light-splitting structures may be coupled to the surfaces of one ormore crystal elements that form a portion of the crystal array. Asanother example, each crystal element 202 may be coupled to one or morelight-splitting structures. The position and dimensions oflight-splitting structures set on each crystal element may or may not bethe same.

FIG. 8 illustrates an example 802 of a crystal element in accordancewith some embodiments of the disclosure. As shown, crystal element 802may have multiple surfaces, such as surfaces 01, 02, and 03. One or morelight-splitting structures (e.g., light-splitting structures 01 a and 02a) may be mounted on one or more surfaces of the crystal element 802. Insome embodiments, the area of a light-splitting structure mounted on asurface of crystal element 802 (e.g., surface 03 that defines a lightoutput surface of crystal element 802) may be smaller than the area ofthe surface of crystal element 802. The areas of the light-splittingstructures mounted on each crystal element may or may not be the same.For example, in some embodiments in which surface 03 may be used todefine a light output surface of crystal element 802, light-splittingstructures 01 a and 02 a may be mounted on surface 01 and surface 02,respectively. The area of light-splitting structure 01 a may or may notbe the same as that of light-splitting structure 02 a. In someembodiments, a light-splitting structure mounted on surface 03 (notshown in FIG. 8) may be smaller than surface 03.

Upon receiving a γ ray at the crystal element 802, the γ ray excitesmultiple photons inside the crystal element 802. In some embodiments,one or more of the photons may enter into a semiconductor sensorcorresponding to surface 03 (e.g., a semiconductor sensor coupled tosurface 03). One or more of the other photons may enter into one or moreother crystal elements of the crystal array through one or more othersurfaces of the crystal element 802 (e.g., surface 01, surface, 02,etc.). The other photons may then transmit between the other crystalelements, and may ultimately enter into one or more semiconductorsensors corresponding to the other crystal elements. In someembodiments, the PET detector may determine the position of photonexcitation inside the crystal elements based on an output of thesemiconductor sensors.

In some embodiments, one or more of the light-splitting structuresmounted on crystal element 802 may be and/or include one or morelight-reflective films and/or white light-reflective coatings on thesurface of crystal element, etc. Each of the light-splitting structuresmay be configured to have a particular size and/or be positioned in aparticular portion of a surface of the crystal element. The number ofphotons that may pass through a given light-splitting structure may bedetermined based on the size of the given light-splitting structure andthe position of the light-splitting structure on the surface. Thedifferent photons numbers further lead to the numbers of photons thateach semiconductor sensor received are different, which ultimatelyaffect the analyzed position results of photons according to the outputof semiconductor sensor. Taking two crystal elements as an example,various configurations of the light-splitting structures coupled to oneof the crystal elements may be used to cause various numbers of photonsexcited in the crystal element to be entered into the other crystalelement.

For example, as shown in FIGS. 9 and 10, the PET detector may includecrystal elements 902 and 904 that are adjacent to each other. Asillustrated using the dash area, a light-splitting structure (e.g., awhite light-reflective coating) is mounted on a surface of the crystalelement 904 that is adjacent to a surface of crystal element 902. Thesurface of crystal element 904 is also referred to as the “contactsurface” herein. In some embodiments, a γ ray may excite multiplephotons (e.g., three photons) in the crystal element 902. When thephotons that are excited inside the crystal element 902 transmit to thewhite light-reflective coating, the photons reflect as an effect of thewhite light-reflective coating, instead of entering into the crystalelement 904 through the white light-reflective coating. In someembodiments, when the photons transmit to a contacting surface which isnot part of the white light-reflective coating, the photons may enterinto the crystal element 904 through the contacting surface which is notpart of the white light-reflective coating.

For example, as shown in FIG. 9, the area of the white light-reflectivecoating may be equal to or greater than that of the contact surface ofcrystal element 902. In such an example, neither of the two photons thattransmit to the contact surface may enter into the crystal element 904.As another example, as shown in FIG. 10, the white light-reflectivecoating covers a portion of the contact surface (e.g., about half of thecontact surface). In such an example, one of the two photons thattransmit to the contact surface may enter into the crystal element 904.

As described above, various configurations of light-splitting structureson surfaces of a particular crystal element may be used to cause variousnumbers of photons to enter into other crystal elements. To clearlyidentify each crystal, the area of the light-splitting structure mountedon a crystal element may be adjusted by adjusting the probability thatphotons appear in a crystal element.

In some embodiments, the probability that photons appear in a selectedcrystal element in the crystal array may be determined using thefollowing formula:

$\begin{matrix}{{{P(m)} = {\frac{N!}{{m!}{\left( {N - m} \right)!}}{p^{m}\left( {1 - p} \right)}^{({N - m})}}},} & (1)\end{matrix}$

where N represents the total number of photons that are excited insideany crystal element other than the selected crystal element in thecrystal array. m represents the number of photons that occur inside theselected crystal element when the total number of photons excited insideany crystal element is N. p represents a probability that when a photonis excited in the arbitrary crystal unit the photon happen to occur inthe selected crystal unit. P represents the probability of the number ofthe photons that occur inside the selected crystal element is m when thetotal number of photons excited inside any crystal element is N.

The area of a light-splitting structure on a crystal element may beadjusted based on formula (1). In some embodiments, one or more valuesof N, m, and P may be determined based on tests and/or experiments. Animage generated by the PET detect may need to have a certain resolutionof crystal elements (e.g., a resolution that is equal to or greater thana threshold) to be used to determine the location in a crystal elementwhere photons are excited, when analyzing the location where photons areexcited according to the output of semiconductor sensors. In someembodiments, if more photons appear inside each crystal element in thecrystal array, the resolution of each crystal element in the image ishigher. When the probability of occurrence of photon inside the selectedcrystal element P meets the resolution requirement of crystal element inthe image, the crystal element will be set according to the area oflight-splitting structure corresponding to the probability P.

A light-splitting structure coupled to the selected crystal element maybe configured based on the probability that photons would appear in theselected crystal element. In some embodiments, a PET detector maydetermine that the probability that photons appear in the selectedcrystal element is higher than a predetermined value (e.g., aprobability that is equal to or greater than a threshold) and mayconfigure the light-splitting structure based on the determination. Forexample, a special machine to assemble PET detectors may reduce the areaof the light-splitting structure on the crystal element. As anotherexample, the special machine may adjust the position of thelight-splitting structure on the crystal element. As still anotherexample, the special machine may reduce the same time and adjust theposition of the light-splitting structure on the crystal element. Insome embodiments, the PET detector may determine that the probabilitythat photons appear in the selected crystal element is not high (e.g., aprobability that is not greater than a threshold) and may configure thelight-splitting structure based on the determination. For example, thespecial machine may increase the area of the light-splitting structureon the crystal element. As another example, the special machine camadjust the position of the light-splitting structure on the crystalelement. As still another example, the special machine may increase thearea of light-splitting structure and may adjust the position oflight-splitting structure on the crystal element.

In one embodiment of this invention, a 1×10 crystal array is assembled,wherein the crystal array includes 10 crystal elements andlight-splitting structures are set on each crystal element. Taking a PETdetector comprising the 1×10 crystal array as an example, a detailedillustration is given on the adjusting of light-splitting structures seton each surface of crystal element according to formula (1).

As shown in FIG. 11 and FIG. 12, FIG. 11 illustrates the probabilitydistribution of photons that appear inside a crystal element in thecrystal array before adjusting. FIG. 12 illustrates the probabilitydistribution of photons that appear inside a crystal element in thecrystal array after adjusting. The horizontal axis in the FIG. 11 andFIG. 12 represents the positioning of each crystal element, in which thewaveform between the two adjacent wave troughs represents theprobability distribution of photons that occur in different positioninginside one crystal element. The vertical axis represents the probabilitydistribution of photons that appear inside each crystal element. Thewaveform represents the probability distribution of photons that occurin the crystal element. If the peak-to-trough ratio of a waveform isgreat, the resolution of crystal element in the image that obtained ishigh.

By comparing FIG. 11 to FIG. 12, it is suggested that most values ofpeak-to-trough ratio of the waveforms that represent the probabilitydistribution of photons that appear in the crystal element in FIG. 12are higher than the corresponding ones in FIG. 11. That is to say, a PETdetector with a higher resolution may be obtained by adjusting thelight-splitting structures set on the surface of a crystal elementaccording to formula (1).

In a specific embodiment, to better satisfy the resolution requirementsof crystal element on images, when setting the light-splittingstructures on the surfaces of crystal elements, light-receiving areas ofthe semiconductor sensors, relative positioning among semiconductorsensors, and relative positioning between semiconductor sensors and thecrystal array may also be used to set the light-splitting structures onthe crystal elements. That is to say, settings of the light-splittingstructures on the surfaces of crystal elements may also need to matchlight-receiving areas of the semiconductor sensors, relative positioningamong semiconductor sensors, and relative positioning betweensemiconductor sensors and the crystal array.

Wherein, the light-receiving areas of the semiconductor sensors mayalready be determined when the semiconductor sensors are dispatched fromthe manufacturer. For example, a conventional semiconductor sensor mayhave a light-receiving area of 3×3 mm² or 6×6 mm². In practice, in orderto further minimize the size of the PET detector, semiconductor sensorswith light-receiving areas of 3×3 mm² may be chosen.

Under common conditions, among the factors of light-receiving areas ofthe semiconductor sensors, relative positioning among semiconductorsensors, relative positioning between semiconductor sensors and thecrystal array, and the probability of photons occurring in each crystalelements, when one or more of the mentioned factors are determined, thePET detector may satisfy the resolution requirements of crystal elementon images by adjusting other parameters of the factors.

For example, when the light-receiving areas of the semiconductor sensorsare determined, relative positioning among semiconductor sensors,relative positioning between semiconductor sensors and the crystalarray, and the probability of occurrence of photon in each crystalelement may be adjusted to satisfy the resolution requirements ofcrystal element on images. When the light-receiving areas of thesemiconductor sensors, and the probability of photons occurring in eachcrystal elements are determined, relative positioning amongsemiconductor sensors, and relative positioning between semiconductorsensors and the crystal array may be adjusted to satisfy the resolutionrequirements of crystal element on images. When the light-receivingareas of the semiconductor sensors, relative positioning amongsemiconductor sensors, and relative positioning between semiconductorsensors and the crystal array are determined, the probability ofoccurrence of photon in each crystal element may be adjusted to satisfythe resolution requirements of crystal element on images.

Therefore, when setting the PET detector in embodiments of the presentinvention, the areas of light-splitting structures on each crystalelements of the crystal array may be adjusted first, and followed by thesemiconductor sensor array being set according to the light outputsurfaces of the crystal. Alternatively, the semiconductor sensor arraymay be set according to the light output surfaces of the crystal first,followed by adjusting the areas of light-splitting structures on eachcrystal elements of the crystal array. Regardless of the order of thetwo, it suffices to satisfy the resolution requirements of crystalelement on images.

When the PET detector is being used to detect the location where photonsare excited, as described above, one crystal element in the crystalarray receives a γ ray, and the γ ray excites photons in the crystalelement. After the semiconductor sensors have received the photons fromthe light output surface of the crystal array, the locations where thephotons are excited by the γ rays in the crystal elements may bedetermined according to the output of the semiconductor sensors.

When determining the locations where the photons are excited based onthe output of the semiconductor sensors and using the center-of-gravityreadout method, the total energy of excited photons (E), the energy ofphotons received by semiconductors in one row (X1), and one of thecolumns of the energy of photons received by semiconductors (Y1) need tobe calculated. By such calculation, the row location of the excitedphotons may be x=X1/E, and the column location may be y=Y1/E. Thelocation where the photons are excited may be determined by the valuesof x and y. Wherein, the total energy (E) of all the excited photons maybe equal to the sum of the energies detected by each semiconductorsensors of the PET detector. One of the rows of the energy of photonsreceived by semiconductors (X1) may be equal to the sum of the energiesdetected by each semiconductor sensors in one of the rows. One of thecolumns of the energy of photons received by semiconductors (Y1) may beequal to the sum of the energies detected by each semiconductor sensorsin one of the columns.

Currently, when determining the location where photons are excited, thecommon procedure is: reading the output data from each semiconductorsensors, and determining the location of photons according to thereadings of data. In other words, when using the above mentionedprocedure, the amount of data read and the number of semiconductorsensors are the same. In such a way, when the PET detector includesmultiple semiconductor sensors, the amount of data processed todetermine the location where photons are excited is increased, andtherefore, the difficulty to determine the location where photons areexcited is also increased. For example, when using a PET detector asshown in FIG. 5 to determine the location where photons are excited,since the PET detector includes 8 semiconductor sensors, the number ofsets of data totals 8 after reading the data from the semiconductorsensors. In further processing to determine the location where photonsare excited, the 8 sets of data need to be processed to determine thelocation where photons are excited, and the difficulty of determiningthe location where photons are excited may be increased.

As a solution to the above mentioned situation, in an embodiment of thepresent invention, when setting the PET detector, the PET detector mayfurther include a first amplifier, and the input terminal of the firstamplifier may be connected with the output terminal of a predeterminedrow of semiconductor sensors in the semiconductor sensor array. Wherein,number of the first amplifier may be set according to the row number ofthe semiconductor sensor array, and number of the first amplifier may beequal to or less than the row number of the semiconductor sensor array.When connecting the input terminal of the first amplifier with theoutput terminal of a predetermined row of semiconductor sensors in thesemiconductor sensor array, each input terminal of the first amplifierare connected with each output terminal of a predetermined row ofsemiconductor sensors in the semiconductor sensor array correspondingly,and each input data of the first amplifier is also an output terminal ofa predetermined row of semiconductor sensors in the semiconductor sensorarray. In such a way, when using center-of-gravity readout method todetermine the location where photons are excited, the output of a row ofsemiconductor sensors may be determined directly according to the outputof the first amplifier, and it is not required to read output of everysemiconductor sensor. The amount of data processed to determine thelocation where photons are excited, and the difficulty to determine thelocation of photons may be both reduced.

In the same manner, when setting the PET detector, the PET detector mayfurther include a second amplifier, and the input terminal of the secondamplifier may be connected with the output terminal of a predeterminedcolumn of semiconductor sensors in the semiconductor sensor array. Fordetailed descriptions regarding setting the second amplifier, referenceshould be made to the descriptions regarding the first amplifier, whichwill not be repeated here.

In practice, the PET detector may only include either the firstamplifier or the second amplifier, or include both the first amplifierand the second amplifier. When the PET detector includes both the firstamplifier and the second amplifier, the amount of data processed whenthe location where photons are excited is determined may be furtherreduced to determine the location where photons are excited, as well asthe difficulty to determine the location of photons.

Taking the PET detector shown in FIG. 13 as an example, an illustrationof the setting and detecting of the PET detector according toembodiments of the present invention is given.

As shown in FIG. 13, the PET detector include crystal elements 202,which are arranged in an 8×8 crystal array, and semiconductor sensors2081-2084, which are arranged in a 2×2 semiconductor sensor array.

When setting the PET detector, after specific semiconductor sensors areselected, the relative positioning among semiconductor sensors2081-2084, and the relative positioning between semiconductor sensorsand the crystal array may first be determined, then the light-splittingstructures on the surfaces of crystal elements may be further adjusted,to satisfy the resolution requirements of crystal element on imagesacquired by the PET detector.

Wherein, when adjusting the areas of the light-splitting structures seton the surface of each crystal element 202, the adjustment may be thearea of the light-splitting structures corresponding to a probability,wherein the probability meets the resolution condition of crystalelements in the image when adjusting the probability of the photonoccurrence inside each crystal element 202. For example, it is possibleto make the probability distribution of the photon occurrence insideeach crystal element 202 reach the probability distribution shown inFIG. 14. After adjusting the areas of the light-splitting structures seton the surface of each crystal element, set the semiconductor sensorarray opposite to the light output surface of the crystal array, the PETdetector may be obtained.

In order to subsequently determine the position of photon generationaccording to the output of the semiconductor sensors more conveniently,it is also possible to set a first amplifier and a second amplifier inthe obtained PET detector. When setting the first amplifier, it ispossible to set in the row where the semiconductor sensors 2081, 2083reside, or to set in the row where the semiconductor sensors 2082, 2084reside, or to set in the row where the semiconductor sensors 2081, 2083reside and in the row where the semiconductor sensors 2082, 2084 resideat the same time. In some embodiments of the present invention, forexample, set the first amplifier 1301 in the row where the semiconductorsensors 2081, 2083 reside. Likewise, when setting the second amplifier,it is possible to set in the column where the semiconductor sensors2081, 2082 reside, or to set in the column where the semiconductorsensors 2083, 2084 reside, or to set in the column where thesemiconductor sensors 2081, 2082 reside and in the column where thesemiconductor sensors 2083, 2084 reside at the same time. In someembodiments of the invention, for example, set the second amplifier 1302in the column where the semiconductor sensors 2081, 2082 reside, and setthe second amplifier 1303 in the column where the semiconductor sensors2083, 2084 reside at the same time.

Wherein, the output of the first amplifier 1301 is out1, and the outputof the second amplifier 1302 is out2, and the output of the secondamplifier 1303 is out3. Thus, the total energy of photons E=out2+out3,wherein the received photons energy by one row of the semiconductorsensors X1=out1, and the received photons energy by one column of thesemiconductor sensors Y1=out2 or Y1=out3. It is important to note that,after determining the one row and the one column, the position of photongeneration may be determined in the coordinates wherein the one row isX-axis and the one column is Y-axis. For example, assume the receivedphoton energy Y1=out2 by the one column of the semiconductor sensors,according to the center-of-gravity readout method, the row of theposition of photon generation x=X1/E=out1/(out2+out3),y=Y1/E=out2/(out2+out3). Thus, the position of photon generation may bedetermined according to the outputs of the first amplifier 1301, thesecond amplifier 1302, and the third amplifier 1303. In comparison todetermining the position of photon generation by the outputs ofsemiconductor sensors 2081, 2082, 2083 and 2084, it effectively reducesthe amount of data processing when determining the position of photongeneration.

By detection simulation by the PET detector, the obtainedtwo-dimensional image analytic results regarding the position of eachcrystal element is shown in FIG. 15, wherein the horizontal ordinaterepresents the position of the columns where each crystal elementresides and the vertical ordinate represents the position of the rowswhere each crystal element resides. It is shown by FIG. 15 that eachcrystal element is arranged evenly, and each crystal element is clearlyvisible, such that the resolution of the crystal elements in the figureis relatively high. The photon positions may be obtained precisely byapplying the PET detector to detect the position of photon generation.

To help those skilled in the art understand and practice the embodimentsof the present invention, the methods corresponding to the PET detectorwill be illustrated below.

As shown in FIG. 16, some embodiments of the present invention alsoprovides a method for setting up PET detector, the method may comprise:

Step 1602: adjusting areas of light-splitting structures set on eachcrystal element in the crystal array.

wherein, when adjusting areas of light-splitting structures set on eachcrystal element in the crystal array, adjusting the probability ofoccurrence of photon in the each crystal element, when the probabilityof occurrence of photon in the each crystal element fulfills aresolution condition of the crystal elements in an image, set thecrystal elements according to the area of the light-splitting structurecorresponding to the probability of occurrence of photon.

When adjusting the probability of occurrence of photon in the eachcrystal element, adjusting the probability of occurrence of photon in aselected crystal element according to the equation (1).

Step 1604: setting the semiconductor sensor array in opposite to thelight output surface of the crystal array, to obtain the PET detector.

It should be noted that, in specific embodiments of the presentinvention, the execution order of Step 1602 and Step 1604 is notlimited. That is to say, it is possible to adjust the areas oflight-splitting structures set on each crystal element in the crystalarray first, then set the semiconductor sensor array in opposite to thelight output surface of the crystal array, or set the semiconductorsensor array in opposite to the light output surface of the crystalarray first, then adjust the areas of light-splitting structures set oneach crystal element in the crystal array; the above description is notlimiting.

When applying the setting method in the embodiments of the presentinvention to set up the PET detector, one may refer to the descriptionof embodiments of PET detectors illustrated above, and furtherdiscussion will not be provided here.

As shown in FIG. 17, embodiments of the present invention also providesa method for detecting with PET detector, the method may comprise:

Step 1702: receiving a gamma ray by a crystal element of the PETdetector.

Step 1704: receiving photons excited by the gamma ray in the crystalelement by a semiconductor sensor of the PET detector;

Among them, Step 1702 and Step 1704 may be executed referring to thedescription of embodiments of PET detectors illustrated above.

Step 1706: determining a position where the gamma ray generates thephotons in the crystal element according to an output of thesemiconductor sensor.

In practice, the location where photons are excited inside the crystalelements by the gamma ray may be determined by the center-of-gravityreadout method, referring to the description of embodiments of PETdetector illustrated above.

Although the present invention is disclosed as above, the presentinvention is not limited thereto. Any skilled in the art, withoutdeparting from the spirit and scope of the present invention, may comeup with various changes and modifications, and therefore the scope ofprotection regarding the present invention should be defined by theclaims.

1. A positron emission tomography (PET) detector, the PET detectorcomprising: a crystal array, the crystal array comprising a plurality ofcrystal elements and a light-splitting structure mounted on a surface ofeach of the plurality of crystal elements, the light-splittingstructures defining a light output surface of the crystal array jointly;and a semiconductor sensor array comprising a plurality of semiconductorsensors for receiving photons from the light output surface, each of theplurality of semiconductor sensors contacting at least a portion of thelight output surface of the crystal array.
 2. The PET detector accordingto claim 1, more than one of the plurality of crystal elements in thecrystal array being coupled with one semiconductor sensor of thesemiconductor sensor array.
 3. The PET detector according to claim 1, atleast one semiconductor sensor of the semiconductor sensor array beingcoupled with each of the plurality of crystal elements in the crystalarray.
 4. The PET detector according to claim 2, the coupling comprisinga contact between the semiconductor sensors and the crystal elementsdirectly or through an adhesive material.
 5. The PET detector accordingto claim 1, a center-of-gravity of the semiconductor sensor arraycoinciding with a center-of-gravity of the crystal array.
 6. The PETdetector according to claim 1, the semiconductor sensor array completelyor partially covering the light output surface.
 7. The PET detectoraccording to claim 1, the light-splitting structure including alight-reflective membrane or a white light-reflective coating.
 8. ThePET detector according to claim 1 further comprising a first amplifier,an input terminal of the first amplifier being connected with an outputterminal of a semiconductor sensor in a predetermined row of thesemiconductor sensor array.
 9. The PET detector according to claim 1further comprising a second amplifier, an input terminal of the secondamplifier being connected with an output terminal of a semiconductorsensor in a predetermined column of the semiconductor sensor array. 10.The PET detector according to claim 1, the light-splitting structures onthe surfaces of the crystal elements being set based on light-receivingareas of the semiconductor sensors, a relative location between thesemiconductor sensors, and relative positioning between thesemiconductor sensors and the crystal array.
 11. The PET detectoraccording to claim 1, a number or positioning of the semiconductorsensors relating to a spatial resolution of the crystal elements in animage.
 12. A method for setting a PET detector, the method comprising:adjusting an area of a light-splitting structure on each of a pluralityof crystal elements in a crystal array, the light-splitting structuresjointly forming a light output surface of the crystal array; and settinga semiconductor sensor array in contact with at least a portion of thelight output surface of the crystal array, the semiconductor sensorarray comprising a plurality of semiconductor sensors for receivingphotons from the light output surface.
 13. The method according to claim12, the adjusting of the area of the light-splitting structurecomprising: adjusting a probability of photon occurrence in a crystalelement of the plurality of crystal elements; determining that theprobability of photon occurrence in the crystal element satisfies aspatial resolution condition to obtain a first determination result;setting, based on the first determination result, the area of thecrystal element according to the area of the light-splitting structurecorresponding to the probability of photon occurrence.
 14. The methodaccording to claim 13, the adjusting of the probability of photonoccurrence in the crystal element comprising: adjusting the probabilityof photon occurrence in a first crystal element according to thefollowing equation:${P(m)} = {\frac{N!}{{m!}{\left( {N - m} \right)!}}{p^{m}\left( {1 - p} \right)}^{({N - m})}}$wherein N represents a total number of the photons excited in a secondcrystal element in the crystal array other than the first crystalelement, m represents a number of the photons excited in the firstcrystal element when N photons are excited in the second crystalelement, p represents a probability that when a photon is excited in thesecond crystal element the photon occurs in the first crystal element,and P represents a probability that m photons occur in the first crystalelement when N photons are excited in the second crystal element.
 15. Adetection method comprising: providing a PET detector according to claim1; receiving a γ ray by a crystal element of the PET detector; receivingphotons excited by the γ ray in the crystal element by a semiconductorsensor of the plurality of semiconductor sensors; and determining aposition where the γ ray excites the photons in the crystal elementaccording to an output of the semiconductor sensor.
 16. The detectionmethod according to claim 15, the determining of the position comprisingusing a center-of-gravity readout method.
 17. A positron emissiontomography (PET) detector, the PET detector comprising: a crystal array,the crystal array comprising a plurality of crystal elements; each ofthe plurality of crystal elements extending along an up-to-downdirection, and having an upper side, a lower side, and a surroundingsurface between the upper side and the lower side; a light-splittingstructure mounted on the surface of each of the plurality of crystalelements, the light-splitting structure corporately with the crystalarray to define a light output surface; and a semiconductor sensor arraycomprising a plurality of semiconductor sensors for receiving photonsfrom the light output surface, each of the plurality of semiconductorsensors sharing at least a portion of the light output surface of thecrystal array.
 18. The PET detector according to claim 17, wherein theplurality of crystal elements have a same length.
 19. The PET detectoraccording to claim 17, wherein the light-splitting structures havedifferent lengths along the up-to-down direction.
 20. The PET detectoraccording to claim 17, wherein the semiconductor sensors are directlycoupled with crystal elements.